1. Field of the Invention
This invention relates generally to a device and method for controlling the flow of material through a conduit. More specifically, the invention relates to a control valve that cuts off the flow of air to a pneumatic tool and a method of using the same.
2. Description of the Related Art
Control valves and similar devices have been used for cutting off and regulating the flow of material through a conduit. For example, it is known to provide a control valve at a desired position along a conduit that has a flow of liquid, gas, or other flowable material therethrough. Normally, these control valves are utilized to begin the flow of material, slop the flow of material, or maintain the flow of material through the conduit at a desired rate. Typically, the control valves are either manually or automatically activated and can be completely mechanical in design, electrical in design or can be designed with a combination of electrical and mechanical components.
Such control valves are frequently used to regulate the flow of compressed air. Compressed air is not only used to drive power tools such as drills, jackhammers, and similar pneumatic tools, but it is used in a variety of other areas including inflating articles, cleaning articles, and in pneumatic conveying. Accordingly, compressed air has been employed as a source of power in a variety of settings.
Compressed air is also used extensively to power pneumatic tools in manufacturing. These pneumatic tools are typically supplied compressed air from an air compressor through a conduit, such as a pipe or hose. Frequently, the compressor is positioned in a fixed location and a system of compressed air supply lines is set up around the work place or factory. The pneumatic tools are then hooked up to the system at desired positions to enable a worker to use a pneumatic tool at a specific location. Normally, in operation, each pneumatic tool is constantly supplied air from the compressor. An operator controls the operation of the pneumatic tool by pulling a trigger or similar actuating device to allow compressed air to flow to and drive the tool.
When pneumatic tools are used in manufacturing, it is common to prescribe performance or quality specifications when assembling a particular part or piece of equipment. For example, when either a screw or bolt is to be tightened, it is important that the screw or bolt is tightened to a specific degree so that it is neither too loose nor too tight. Therefore, manufacturers frequently specify a desired rotational tightening force or torque to be employed on a particular item that is being assembled. Since these torque specifications are difficult for an operator to achieve with a manual tool, power tools, including pneumatic tools, are normally employed to achieve the desired torque specifications.
In order to obtain a desired torque with a pneumatic tool, a shut off or control valve is normally employed to automatically shut off the flow of air to the pneumatic tool upon reaching a certain torque. The torque can be measured by the pneumatic tool itself or by a separate device in communication with the pneumatic tool. In either event, upon attaining the desired torque, a signal is generated and transmitted either directly to the control valve or to a central control unit that in turn activates the control valve to shut off the supply of compressed air and stop the pneumatic tool. Of course, it can also be desirable to control other pneumatic tool outputs with a control valve other than the torque of a rotational pneumatic tool.
Control valves that are used to shut off the flow of compressed air to a pneumatic tool normally employ a solenoid type mechanism. The solenoid mechanism receives a signal from the pneumatic tool or a central control unit that energizes or de-energizes the solenoid mechanism to open or close the valve accordingly. These control valves typically have a valve seat that is sealed by a spring loaded solenoid plunger member in its at-rest position to prevent air flow through the control valve. To initiate air flow through the control valve, the spring loaded solenoid plunger member is moved away from the valve seat against the force of the spring by the solenoid's electromagnet that is energized by the signal.
Frequently, the forward flow of compressed air through the solenoid type control valve to the pneumatic tool combines with the force exerted by the spring to provide an additional force to hold the spring loaded solenoid plunger member against the valve seat. Consequently, to open the valve, the solenoid's electromagnet must be powerful enough to move the spring loaded solenoid plunger member against both the force of the spring and the force of the forward air pressure. Electromagnets having this power capacity are frequently to large for many environments and usually require a larger power input in order to be activated.
Additionally, in practice, the control valve is sometimes positioned along the length of the conduit at a distance from the pneumatic tool. This is especially true when a multi-spindle pneumatic tool is being used where there is no room for the valve near the tool itself. The main problem that exists with this type of pneumatic tool is that after the control valve shuts off the air flow, air remains in the line between the valve and the tool. Accordingly, due to the remaining air, the tool continues to operate after the control valve is shut off. This condition is completely undesirable since it prevents a precise shut down of the pneumatic tool and a particular, exact torque specification from being achieved.
Accordingly, there is a need for an improved control valve that is simple and compact in design, efficient to operate and can provide a complete, immediate shut down of a tool regardless of its position in the system.